This invention pertains to rubber-metal composites formed by applying a layer of an autodeposited coating on a metal surface and then directly bonding rubber to the coated metal surface. The use of a separate adhesive or binder layer is not required.
Rubber-metal composites are widely used in the manufacture of anti-vibration (AV) and noise and vibration handling (NVH) components. Such components are most commonly used as engine mounts in vehicles and as oil seals for rail cars. Typically, the rubber used is natural rubber (NR) for AV and NVH components and nitrile rubber (NR) for applications where resistance to oil and grease is required. Traditionally, the rubber is bonded to a preformed metal substrate which has first been phosphated. Phosphating of the metal is critical since it protects the metal surface from corrosion and prepares it for bonding to the rubber. However, phosphate pretreatment has the disadvantage of generating large volumes of effluent waste which must be treated prior to disposal. Elimination of the phosphating step thus would be desirable, although some alternative method of imparting corrosion resistance to the metal surface must still be used. Rubber-metal composites, particularly those utilized in automotive applications, are exposed to substances containing corrosive salts or the like that may attack any metal surface not covered by the rubber and/or the bond between the metal and rubber components.
The phosphated metal surface is then commonly bonded to the rubber using two coats of adhesive (a primer coat and a top coat). The primer coat bonds primarily to the phosphated metal, while the top coat bonds to the rubber. Most of the adhesive used currently in the industry for this purpose are solvent-based and have a high content of VOCs (volatile organic compounds). Commonly used solvents are toluene, xylene, and methyl isobutyl ketone (MIBK).
The use of autodeposition coatings in rubber-metal composites is described in WO 99/30841 and WO 99/37713. Such coatings provide good corrosion protection to metal substrates, thereby permitting the phosphate pretreatment step to be eliminated. However, to date such coatings have always been used in combination with one or more layers of an adhesive or binder.
This invention provides a method for bonding an elastomeric substrate surface to a metallic substrate surface comprising autodepositing a coating onto the metallic substrate surface, contacting the elastomeric substrate surface with the coating on the metallic substrate surface, and forming a bond between the elastomeric substrate surface and the metallic substrate surface. Application of a separate adhesive layer or separate primer layer to the autodeposited coating prior to bonding thus is not necessary.
This process is simpler and more economical to operate than conventional methods of bonding rubber to metal, yet provides a rubber-metal composite with excellent adhesion between the rubber and metal components. The process has the further advantage of not requiring the use of an organic solvent-containing adhesive, thereby lessening environmental problems. If the autodeposited coating is pigmented, the rubber-metal composite need not be painted with a final top coat after assembly since the appearance of the autodeposited coating is adequate for most industry requirements.